Inflatable boats are a popular alternative to rigid hulled boats. Inflatables offer the ability to be easily stored or transported when deflated and an extremely high degree of buoyancy when inflated. They are commonly horseshoe shaped and have either a rigid transom or an additional inflatable portion at the stern. These boats can be used to transport from 1, to in excess of 30 people depending on the boat's size. Inflatable boats are used as weekend craft, dinghies for larger boats or as survival craft such as life rafts.
Typically, an inflatable boat will employ at least two inflatable chambers to form the craft's horseshoe shape and a wooden connecting plank at the rear to form the transom. The bow is formed in the region where the forward ends of the inflatable chambers abut. The bottom of the boat is normally formed from a flexible plastic material whose outer edges are affixed to the inflatable chambers.
Inflatable boats, while providing a number of distinct advantages, suffer from a number of problems inherent to the materials involved and the overall design of the craft.
These boats are normally flat-bottomed and do not have a depending keel due to the flexible nature of the bottom material. Without a keel, these boats have minimal directional stability. This lack of stability is most apparent during turning maneuvers when excessive slippage is normally experienced.
An inflatable boat's air chambers are critical to the safety of the craft, yet they are jeopardized by conditions which the boats commonly experience. Inflatable boats are often beached and thereby are subject to abrasion damage. They are used in shallow or protected waters (bays, harbors, marinas, etc.) where the probability of contacting floating debris is great. The inflatable chambers typically employ at least one layer of flexible material to form the sides of the chamber and most commonly, a multi-layered construction is used. However, due to the inherent flexibility of the materials used, puncture or heavy abrasion of the chambers continues to be a real concern. Floating debris can act like a knife to cut the chamber walls when the craft is traveling at a high speed. Numerous beachings of the boat can eventually wear through the wall material or at least considerably weaken it. Therefore, the integrity of the inflatable chambers is often at risk and concerns for this problem have led substantially every manufacturer to include in their boats a plurality of separate, air filled chambers in lieu of a solitary chamber.
The inherent flexibility of the boat and the materials that make up its water contacting surface leads to another significant problem with this type of craft. A considerable amount of horsepower is required to bring the boat to planing speed. This is due to frictional resistance between the boat's bottom surface and the water, the flexible nature of the boat's bottom which creates a non-planar surface during acceleration and actual bending of the boat. As the outboard engine provides thrust, the bow of the boat lifts and thereby causes the bottom of the front portion of the boat to act as a plow and thereby greatly increase the drag forces on the boat. Besides increasing the power requirements, the above noted factors all adversely affect the fuel economy of the craft.
An additional handling characteristic of inflatable boats that is undesirable is the rough manner in which the bow of the boat cuts a wave. When an inflatable boat is being propelled at even a minimal speed into a wave, its bow tends to break the wave. Most rigid boats have a relatively sharp bow and, upon contacting a wave, the bow cleanly cuts through it. In this way, rigid craft avoid or minimize the considerable shock that can result should the bow not cut the wave. Most inflatable boats have somewhat a "V"-shaped bow, but the front "cutting" edge is blunt at best. When an inflatable boat contacts a wave, the bow poorly cuts the wave and a considerable impact results and is sorely felt by the boat's occupants. In addition, a substantial amount of spray also results during a hard impact further adding to the discomfort of the boat's passengers. The resilient nature of the inflatable chambers further exacerbates the problem since the bow tends to flatten during impact thereby increasing its frotal area and further blunting its cutting ability.
To overcome some of the noted problems with inflatable boats, a number of hybrid boats have been patented. These boats have a traditional rigid bottom and use inflatable chambers as sides. These boats do not enjoy the easy portability and low cost of conventional inflatable boats. Craft of this sort can be seen in the patents issued to Cochran (U.S. Pat. Nos. 4,660,497 and 4,498,413).
In a recent effort to solve the noted problems with inflatable boats, Bellia received a patent (U.S. Pat. No. 4,858,550) for a rigid, keeled bottom that can be attached to an inflatable boat. This device uses straps at its front and back for attaching it to the bow and stern of the inflatable boat. As can be seen in FIG. 5 of the patent, the bow of the inflatable boat rests atop the device and requires the addition of a bow strap retaining means to the inflatable boat. The Bellia rigid bottom also extends the length of the boat and is not adaptable to different length boats.